1.CAG codes for the amino acid glutamine, so people with Huntington disease patients will have 36 or more glutamines in a row in the huntingtin protein.
2.The specific way in which extra glutamines causes the disease's symptoms isn't fully understood but the abnormal protein seems to aggregate within the neurons of the cerebellum and the spinal cord, causing them to die.
3.In some cases, the involved gene contains a triplet repeat where the nucleotides C, A and G are repeated multiple times in a row and since CAG codes for the amino acid glutamine, the encoded protein will have multiple extra glutamines in a row.